Radiometric titration method



j. 23, 3945. A LANGER I RADIOMETRIC TITRATION METHOD Filed NOV. 23, 1940 WITNESSES:

Alois Langer.

BY 7W @attested om is., i@

ere-.irse reverie ariete iFeuers Alicia Langer, Forest liiils, Pa., assigner to Westirigieouse Electric it liloiziuiacturirig iompariy, East Pittsburgh, les., a corporation oi Eemisvivauie dgurlieetieii November 23, mail, Seriali No. 35i-5,55%

{@i. Zwtl inve-etico. reist-es carrvirig out che Tire que-otite" ci chemical present in the eclu tion is calculated from the quantity ci the cor responding rea-ecrit ou tire basis of the chemical equations governing precipitate reaction. in carrying out the calculations, the oueutity ci reagent required to completely precipitate o chemical from soiutioumust be knows accurateis. The reagent is customarily added to tice solution in small increments until the precipitation is complete. is tire reagent is added more and more soiid is precipitated until e point is reached at which the small increment of reagent edded passes into solution and does riot produce a precipitate. This point is delued es the ende point of the reaction.

in accordance with the teaching of the prior art of which i am essere, the end=poiut may be determined visually bv observing when no further precipitatiorioocurs on the addition of a reagent or by noties a change in the color or compost tion of the liquid. it may also be dete :red bv observing; vviietlier the resultant solution is' basic or acid, and for this purpose electrical methods may be used. Prior art methods of deter end-point iri general require a, substantial tit? of the substance under observation as they do not apply, conveniently, where only weak solutions are avaliable it is an object of my invention to provide a method ior accurately determining the end-point of a reaction.

Another oioicct ci my invention is to provide a facile precision' method for e the eudpoimt ci a reaction..

'A iurtlier object'oi. my invention is to provide a reliable method for detelning the end-point ci* a reaction involving vveais solutions.

A still further object of my invention is t0 provide simpie and inexpensive apparatus for making end-point determinations.

Au ancillary object ci my invention ls to provide a device for accurately measuring the radioactivity of a liquid.

In accordance with my invention, the endpoint o a reaction is determined by observing the chances iii the radioactivity of one ci the resultents of tice refriction.v reiereiiir the resultarit solution is iii tile eue-ivres most frequently encountered, the originali sciution does riot' contain a radica active eiemerit. A radioactive reagent' is utilized tu this ease in the-practice oi my invention. The reagent is added to the solution bv small incre meritsA and tire radioactivity of the resultant soluu tion is measured. .es loris; se the reagent corr stitutes a portion of the precipitate which is brought dorm. tire liquidie riot radioactive. The liouid only became radioactive when rio further precipitate is produced, i. egtvlieii the end-point is reached.

On occasions the element in the original solu= tion which is to be precipitated is radioactive or may be made radioactive. iu suoli an event a mori-radioactive reagent may ice added. The ra-I dioactivity of the solution their decreases as the radioactive element isprecipiteteol until at the end-point it contains no appreciable amount of the radioactive component, and the radioactivity indication becomes zero.

Where the original solution arid tbe reagent are both radioactive the endpoint is observed by noting when the'additiori or am increment of reagent no longer results in a decrease in the observed radioactivity but iii ari increase.

If neither the reagent oor the solution under observation are originally radioactive, one or the .other may be rendered radioactive by the addition of a small quantity oi a radloactive'element which takes part in' the reaction. The radioactive element must, of course, be added in such a way that it is homogeneously distributed throughout the reagent or the solution. For example, if the reagent is a non-radioactive solution, the radioactive element must be added in a compound which passes into solution. The same situation arises when the solution under observation is to be made radioactive.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended cl. The invention, itself, however, both as to its organization and its methods of operation, together with additional objects and advantages thereof, will best be understoodA from the following description of a specic embodiment when read in connection with the accompanying drawingJn which:

Figure i is a diagrammatic view oi a preferred embodiment of my invention;

Fig. 2 is a graph vsliovviiigiiow the end-point is determined when the reaemt only is radioactive;

f Fig. 3 isa graph showing how the end-point is determinedwhen the original solution only is radioactive; and

Fig. i is a graph showing how the end-point is determined when both they reagent and they original solution are radioactive.

The apparatus shown in the drawing comprises a container 5 in which the solution 'el under observation is disposed. The solution il may take f any any convenient form. The solvent may be 'ponentf of the analysis'may'be measured, theV preferred practice in accordance rwithr myr invenf tionfis to measure the 'resultant liquid as this 'fprocedure does not involve'segregation of the precipitate. The measurement is preferably made by observing the ionization produced by radioactive'idisintegration in a gas at a low pressure. For this purpose, I provide an evacuated tube i3 f preferablyo cylindrical structure containing an inert gas such as argon, at a Ipressure of ytheorder of ten centimeters of mercury. The pressure of the inertfgas is not critical and may vary over ay relatively Wide range. However, a suicient quantity of the gas is required to assure'that ionization occurs when a detectable radioactive disintegration takes place. ,A wire yit extendsy longtudinallythrough the tube and is encircled 'by a conducting shell il, which may be mounted in engagement with ther Wall of yther container i3 or may be a coating on the Wall of the container.

The container is enclosed by a jacket i9 which preferably, but not necessarily,y completely enrate at which the ionization impulses are produced. As previously indicated, such a, measurement is made after each addition of the reagent to the solution, the liquid being returned'irom jacket lil to the container 5 before the next addition of the' reagent, so that a plurality of meter indications `is obtained.` The indicatlons'of the meter are then plotted as the reagent, is added in small increments, yand the end-point is determined by observing forwhat quantity of reagent f f f the critical point in the curves occurs.

In measuring the radioactivity, the readings should, of course, be corrected for the increased volume produced by adding the reagent. The actual radioactivity is given by the equation:

Actual nctlvity=measurod activityX Original volume--edded reagent volume Original volume Typical curves are reproduced in Figs. 2, 3 and c. Ii theforiginaly solution is not radioactive and the reagent'is radioactive, the reagent, when it is first added, passes into the precipitate. There-y f y f fore, the resultantliquid is originally non-radioactive. 'The end-point is reached when theliquid The situation is exempli-r f f becomes radioactive. fled in analyzing for chlorine, forexample, in a potassium chloride solution by adding silver rnitrate which contains radioactivek ions of silver.r f

The additiony of the silver nitrate precipitates silverchloride.y The end-pointis yreached when the solution contains no more chloride toprecipitate ythe silver radical. At this point the solution yis rendered radioactive by the presence of the radioactive ions of silver. The plot for determining the end-point where the'rea'gent' is radioactive and the original solution is non-radioactive is reproduced in Fig'.r k2.

' Radioactivity is plotted vertically and the quancircles it. Near one end a tube 2l, which I may s y designate as the in-fiow tube, extends from the jacket I9 in communication with it. The tube 2i is widened at its extending end so that it has the form of a funnel and the mouth of the funnel is closed by a porous plug 23 pervious to the liquid of the solution but not to any precipitate. In the practice of my invention, the plugged end o the tube 2l dips. into the solution. At the opposite end, the jacket is provided with a second communicating tube 25, which is open to the atmosphere. By exhausting the air from the jacket through the second tube 25, the liquid l is drawn into the jacket i9 through the plug 23 in the inow tube 2l and completely encircles the shell i7.

A ypotential is impressed between the shell il and the wire l5, and when radioactive reactions produce ionization in the container, current impulses flow between the shell and the Wire. The impulses are impressed in the input circuit of a thermionic amplier 21 and the output of the amplifier energizes a meter 29. The meter may indicate the rate at which the ionization impulses are produced or its indicator may merely kick to indicate that an ionization impulse has been produced. in the latter case, the observer may determine the rate by timing-the kicks In either case, a measurement of the radioactivity is attained by observing the rate at which the impulses areproduced.

Thus, a measurement of the radioactivity of the solution. is made by drawing liquid from the container 6 into the jacket I9 and observing the ltity of radioactive reagent is plotted horizontally.

The resultant graph 3| initially extends along the 'abscissaf 33. For ya certain quantity of reagent,

it rises above the axis. yThe end-point ris the f point 35 where the graph is just above the absclssa.

The plot for an originally radioactive solution and a non-radioactive reagent is reproduced in Fig. 3. In this case, the radioactivity first decreases until at the end-point it disappears because the radioactive element has passed completely into the precipitate. The corresponding graph 3l extends from a point along the ordinate 39 to a point 4I along the abscissa 33 and then extends along the abscissa. The end-point is the point 4I at which the graph 31 meets the abscissa 33. The reaction which is represented may be illustrated by the analysis of a. silver nitrate solution containing a radioactive silver isotope for silver by adding potassium chloride. The silver including the radioactive component is precipitated as silver chloride.

The situation, when both the reagent and the original solution are radioactive, may be illustrated by the analysis for uranium of uranyl nitrate (UO2(NO3)2) in an ammonium chloride solution by the addition of a reagent, sodium phosphate (Nazi-IPOD. The resultant precipitate is given by the formula UO2NH4PO4. The uranium is in this case, of course, radioactive and the phosphorus in the reagent is radioactive. In such an event the radioactivity initially decreases as the reagent is added until the uranium has lbeen completely preciptated. At this point the radioactivity is small. Addition cianother increment of the sodium phosphate inj- @,Sditid@ creases the radioactivity. The end-point is that l point d3 of the graph d5 shown in Fig. d where the graph just begins to represent an increasing function.

Although I have shown and described certain specic embodiments of my invention, I am fully aware that many modications thereof are possible. My invention, therefore, is not to be restricted .except insofar as is necessitated by the prior art and by the spirit of the appended claims.

l. claim as my invention:

i. The method of determining the end-point of a reaction when a solution is subjected to the inluence of a reagent, at least one of the components of the reaction being radioactive, whichA comprises mixing small increments of said reagent with said solution and measuring the radioactivity of one of the resultants o the reaction afr each increment is added to determine a point at which an abrupt change in said radioactivity occurs.

2. The method of determining the end-point of a reaction when a solution is subjected to the iniiuence of a reagent which comprises adding a small quantity of a radioactive ions of one of the elements involved in the reaction to the substance in which said elementI is originally present, mixing small increments of said reagent with said solution and measuring the `radioactivity of one of the resultants of the reaction after each iny,

- a reaction when a solution which does not contain a radioactive element is subjected to the inuence of a radioactive reagent which comprises mixing small increments of said reagent with said solution and measuring the radioactivity of the resultant solution after each increment is added to determine a point at which said resultant solution becomes radioactive.

5. The method of determining the end-point of a reaction when a solution is subjected to the infiucnce of a radioactive reagent, said solution con. taining a radioactive component which is precipitated by said reagent, which comprises mixing small increments of said reagent with said solution and measuring the radioactivity of the resultant solution after each increment is added to determine a point at which the radioactivity of said resultant solution passes from a decreasing to an increasing function of the quantity of reagent added.

6. rl'ie method oi determining the end-point of a reaction when a solution is subjected to the influence of a non-radioactive reagent, said solutlon containing a radioactive component which l is precipitated by said reagent, which comprises ment in said. reagent to said reagent, mixing small increments of said reagent with said so lution and measuring the radioactivity of one of the resultante of the reactionafter each increment is added to determine a point at which an abrupt change in said radioactivity occurs.

8. The method of determining the end-point of a reaction when a solution is subjected to the inuence of a reagent which comprises adding a small quantity of a radioactive ions of an element in the original solution, to the original solution, mixing small increments of said reagent with said solution and measuring the radioactivity of one of the resultants of the reaction after each increment is added to determine a point at which 45 an abrupt change in said radioactivity occurs.

ALOIS LANGER. 

